Process of and apparatus for thermometric analysis

ABSTRACT

Process and apparatus for thermometric analysis in which a pump supplies a test solution containing a component, the concentration of which is to be determined, and a reagent solution, adapted to react with the component, to a reaction vessel containing a stirrer and a temperature sensor. The solutions are fed at controlled, constant rates to the reaction vessel through tubing immersed in a constant temperature bath, and the reaction vessel, consisting of a material having a relatively low thermal conductivity, is also immersed in the bath. The temperature in the reaction vessel on mixing the solutions is noted and compared with calibration data.

United States atent Peuschel et al.

[ 1 Feb. 13, 1973 PROCESS OF AND APPARATUS FOR THERMOMETRIC ANALYSIS[73] Assignee: Kali-Chemie A. G., Hannover, Germany Filed: Dec. 4, 1970Appl. No.: 95,153

[30] Foreign Application Priority Data Dec. 9, 1969 Germany ..P 19 61633.2

[56] References Cited UNITED STATES PATENTS 12/1964 Wasilewski ..23 25310/1966 Cooper, Jr ..23/23O OTHER PUBLICATIONS Zenchelsky, ThermometricTitration, Analytical Chemistry, Vol. 32, No. 5, April 1960, pp289R-291R.

Primary Examiner-Morris O. Wolk Assistant ExaminerR. E. SerwinAttorney-Michael S. Striker [57] ABSTRACT Process and apparatus forthermometric analysis in which a pump supplies a test solutioncontaining a component, the concentration of which is to be determined,and a reagent solution, adapted to react with the component, to areaction vessel containing a stirrer and a temperature sensor. Thesolutions are fed at controlled, constant rates to the reaction vesselthrough tubing immersed in a constant temperature bath, and the reactionvessel, consisting of a material having a relatively low thermalconductivity, is also immersed in the bath. The temperature in thereaction vessel on mixing the solutions is noted and compared withcalibration data.

14 Claims, 2 Drawing Figures PATENTEDFEBI 31m 3,716,333

RECORDER v f mamas-r47 2 PUMP INVENTOR 609 P8030? BY m/rz "n w.

PROCESS OF AND APPARATUS FOR TIIERMOMETRIC ANALYSIS BACKGROUND OF THEINVENTION Methods of analysis, in which the measurement of a temperaturechange resulting from a chemical reaction have been used to estimate thecontent of an ingredient have been known for a long time. A variety ofmethods has been used for this purpose, such as, for example, titrationwith thermometric determination of the end point or the addition of areagent solution in excess and measuring of the temperature before andafter the reaction. Physical effects have also been used in this waywhere the temperature change is due to heat of dilution. For completedetection of the temperature change and for elimination of outsidevessels it has been the practice to operate in Dewar vessels or invessels made of thermally insulated synthetic resins. Fundamentally, theobjective was to avoid heat exchange with the surroundings.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of the specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showingthe means for bringing the test solution and the reagent solution to thereaction vessel and recording equipment for measuring and recording thetemperature change resulting; and

FIG. 2 is an elevation in cross-section showing the reaction vessel andits various fittings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS By means of the presentinvention it is possible on the basis of thermometry, to carry out largeseries of analyses automatically and with a high frequency of testing.In addition, the invention is adapted for continuous monitoring andregulation of manufacturing processes. FIG. 1 shows the stream of thetest solution 1 as well as the reagent stream 2 which is generallysupplied in excess by means of a dosing pump 3 through aconstant-temperature bath 4 to a reaction vessel 5 which is alsoimmersed in the bath. The reaction between the two streams takes placein the reaction vessel. The reaction mixture is removed from the vesselthrough the effluent tube 6. The temperature change in the cell dependson the concentration of the component to be estimated. The temperaturechange is measured with a suitable sensor 7 and recorded by the recorder8. In accordance with the present invention, it is possible to measureboth the temperature of the bath and the temperature in the cell.However, it is preferable to hold the bath temperature constant, atwhich point it becomes necessary only to measure the temperature in thecell.

A characteristic of the present invention which contrasts with theconventional processes is that the reaction vessel is in heat exchangewith the constant temperature bath. As a result, the followingadvantages are derived: 1. the effect of room or ambient temperature onthe reaction vessel is eliminated by means of the constant temperaturebath. 2. As a result of introducing the test and reagent solutionslikewise through the bath, the two solutions enter the reaction vesselat equal, and constant temperature. As a result of introducing the twosolutions in a constant ratio, the determination becomes very simplesince the temperature change in the cell is dependent only on changes inconcentration of the component whose concentration is to be determined.The temperature change is measured by means of a sensor and, by means ofa combination of measuring equipment and recorder, is recorded andcompared with previously derived calibration data. The previouslyderived calibration data may be expressed in terms of characteristiccurve.

The advantages of the method become especially clear, when one considersthat in the absence of the thermostatic bath it would be necessary tomeasure three different temperatures, namely, the test and reagentsolution temperatures and that of the reaction mixture. In addition, arelatively complex calculation operation would be necessary to correlatethe temperatures of the solutions and the reaction vessel with thequantity of the substance to be determined in the feed solution. Usingthe present invention, where the bath temperature is held constant, onlyone temperature measurement is necessary. This is achieved in verysimple fashion by using a constant temperature bath of sufficientlygreat volume. In the Examples given below, two constant temperaturebaths in series were utilized to bring the reagent stream and the teststream to the desired temperature. The temperature of the water bathvaried by less than 0.0lC. As is obvious, one constant temperature bathof sufficient size would be adequate for this purpose, the principalrequirement being that a sufficient area of tubing immersed in the bathbe provided so that the streams are completely equilibrated at thetemperature of the bath. For the same reason, the material of which thetubing is composed should, preferably, have a high thermal conductivity.Metals such as copper, steel, nickel and silver meet this requirement.

3. The reaction vessel employed in accordance with the invention ispreferably made of a material with a relatively low thermalconductivity, such as glass, or synthetic resin. The reason is that ifthe thermal conductivity were high, the heat developed during thereaction would be rapidly dissipated through the walls to the constanttemperature bath and the measured temperature change within the vesselwould be too low. Under the stated conditions, it is convenient that theheat exchange with the bath is such that the equilibrium temperature inthe cell is quickly attained. This is necessary so that analysis for thedesired component can be carried out with sufficiently high frequency.This is particularly important, if the component to be determined ispresent in very high concentration so that the analysis has to becarried out in a broad range of percentages. When carrying out theoperation according to this method, a base-line is present whichcorresponds to the region of the lower level of concentration and peaksare recorded. This results in an alternation between the base solutionand the test solution and thereby a relatively high change intemperature in the vessel. In the absence of the bath it will benecessary that the measuring vessel have a high heat capacity in orderto screen out outside influences. The temperature equilibrium on thebasis of the permanent output and loss of heat through the cell wouldtake too long to be established, especially since the thermalconductivity of the vessel material must naturally not be too great.

A further important characteristics of the present invention lies in thestructure of the reaction vessel. The vessel is completely sealed and isconstructed of a material with a relatively low thermal conductivity andfitted with at least two inlets for the test and reagent solutions andwith an exit tube for the reaction mixture. A sensor projects into thevessel for the measurement of temperature, said sensor preferably beinga thermistor; the vessel also contains a high speed stirrer. Preferably,a magnetic stirrer is used, where the drive for the stirrer is locatedbelow the constant temperature bath. In general it is desirable that thevolume of the reaction cell lie between 0.5 and ml., though definitelimits must not be applied to the value. The cells used in the exampleswhich follow has a content of 1 ml.

The indispensible thorough and rapid mixing of the solutions isguaranteed by means of intensive stirring. In addition, the shape of thevessel is such that settling of a precipitate or stoppage as a result ofprecipitation are avoided. Without such stirring, the mixture of thesolutions is incomplete and there is danger of formation of deposits andplugging so that reliable measurements of temperature according to theexperimental design presented is not possible. FIG. 2 shows in elevationa reaction vessel suitable for a precipitation reaction, the scale being5:1. The walls of the lower cylindrical portion 9 and the bottom consistof friction resistant Teflon. The material of the cover 10 is Plexiglaswhich makes it possible to observe the interior of the vessel. The cellcontains a Teflon stirrer consisting of a circular disk 11 in which abar magnet is embedded, and four stirrer vanes 12 placed at right anglesto each other, which provide intensive mixing of the entire volume ofthe cell. The stirrer vanes contain indentations 13 into which thetemperature sensor 7 projects so that in a precipitation reaction thetemperature sensor is maintained free of deposits. The test and relatedsolutions are introduced through at least two tubes 14 into the lowerpart of the cell. The solution inlets may, if desired, be distributedaround the periphery of the vessel, either near each other or atpositions separated by 180. The reaction mixture leaves the vesselthrough the outlet 6 which is connected with the pipe 15.

It is to be understood that the form and the material of the describedreaction vessel had been given merely as an example. Reaction vessels ofother types made of other materials may also be employed.

When the substance whose concentration is to be determined is present inhigh concentrations relative to other components and when the method ofanalysis involves a precipitation reaction, then it is essential thatdifficulties due to the presence of large quantities of solids beovercome. In this case, only relative small errors in the usualtolerance of the analysis are permitted, the precision requirements ofthe analysis will therefore be relatively high. This can be the caseonly if the temperature change is as great as possible, which againmakes it necessary to use high concentrations in the test and reagentstreams which will cause the production of large quantities ofprecipitate. Any dilution used to overcome the effect of the solidsuspension reduces the temperature change and thereby the sensitivity ofthe method. In addition, disturbances from outside influences such asthe unavoidable oscillations of the temperature of the constanttemperature bath-independent of the temperature change in the reactionvessel-remain approximately constant in size. The errors produced bythese disturbances are approximately inversely proportional to thechange in quantity per unit of volume or to the concentrations of thetest and reagent solutions.

ln accordance with the process described above, quantitativedetermination of a component can be effected by means of a heat effectsuch as a heat of reaction which is associated with a sufficiently rapidchemical or physical-chemical process. By this method, neutralizationand dilution heat effects as well as the generally large heat ofreaction of a redox process can be used. Likewise it is possible tocarry out the process on the basis of the heat effect of a precipitationreaction. It is especially favorable for carrying out the desiredprocess that suspensions having a high solids content can be pumpedthrough the vessel.

It is obvious that thermometric analysis in accordance with the presentinvention can easily be rendered automatic. This arrangement leads to asubstantial saving in time and labor.

A further advantage of the process is to be seen in the fact that it isparticularly suitable for analyses of compositions where the content ofthe component whose concentration is to be determined lies in the middleor high percentages. Other methods of physical analyses such as flamephotometry and colorimetry which are suitable for automatic analyticaltechniques, are frequently unsuitable for use at those concentrationlevels.

A further factor in rendering the present process suitable for a widerange of uses is the face that extensive series of individual analysescan be carried outsuch as use in combination with commercial samplechangers-as well as in monitoring continuous test streams. This last isan importance in the automatic monitoring and regulation of processes.

EXAMPLE I The precipitation of potassium according to the equation KC10- KCIO is associated with a substantial positive heat of reaction,which makes it possible to effect a quantitive determination of theelement in accordance with the present process.

By means of a hose'dosing pump, 2.1 ml./min. of test solution (about 12g of potassium salt per ml. of solution) and 1.6 ml./min. NaClO-solution (50 g NaClO, per 100 ml. of solution) were pumped throughsuitable glass spirals immersed in a constant temperature water bath (23i 0.0lC.) and united in a Plexiglas reaction vessel, also located in thesame constant temperature bath. Mixing in the cell was carried out bymeans of a Teflon stirrer with a bar magnet set therein, the stirrerbeing rotated 1,500 revolutions per minute by means of a magneticstirrer located beneath the constant temperature bath.

The difference in temperature generated between the interior of thereaction vessel and the temperature of the bath is proportional to thepotassium content. Since the bath temperature is kept constant, it isonly necessary that the temperature change in the cell be noted,preferably by means of a thermistor, the electrical resistance of whichis dependent on temperature, and to measure the temperature change bymeans of a modified wheatstone. bridge, the temperature being recordedby means of a recorder.

To determine the actual content of the component, the temperature changeis compared with calibration data obtained by measuring the temperaturechange resulting from solutions of known concentrations. The processdescribed was used for the determination of the potassium content in asolution containing a high percentage of potassium fertilizer salts. Thetests were made of a frequency of 30/h. The reproducibility of theanalytical results was extraordinarily good. The error amounted to 02.%KO absolute with a statistical realiability of 95 percent. Systematicdeviations were not found.

It was recognized that glass, of which the spirals were made,vdoes nothave a high thermal conductivity. However, the area of the spirals waslarge and the temperature change involved in the equilibration wassmall. Consequently glass could serve as the material for the spirals.Glass is particularly suitable for such use since it is relatively inertand could not contaminate the solutionswhich were put through it.

EXAMPLE ll In the manufacture of potassium by the hot solution processthe degree of saturation of the solution is of great importance withrespect to optimization of processes.

For control purposes, a continuous stream of about 230 g KCl per litercontaining solution was pumped from a downstream clarifier by means of ahose pump and diluted 1:1 with water. The solution obtained in this waycorresponded in its KCl content with the test solution of Example I. Itwas introduced into the analy-' sis apparatus in a continuous stream of2.1 ml./min. and analyzed as in Example I. By means of the diagramrecorded on the recorder, it is possible to effect regulation of thedegree of saturation of the-potassium salt or the introduction of lye inthe lixivation, apparatus.

EXAMPLE Ill troducing into the measuring cell thermostated streams of anammonia alkaline solution of magnesium salt and ammonium or alkalinedihydrogen phosphate solution. The working out of the recorded measuredvalues is-effected with the help of characteristic calibration curves.

These methods can be used with advantage for the determination ofmagnesium in high percentage magnesium salts and for the continuoustesting of brines such as in the preparation of potassium sulfate and inother processes where the rapid determination of magnesium content insolutions is of importance.

As a reciprocal method of analysis, the ammonium magnesium phosphateprecipitation can be used in a similar way for the determination ofphosphates, by bringing together solutions of the phosphate to bedetermined and a magnesia solution.

The magnesia solution is prepared as follows: 5 g MgCl -6 H 0 and 10 gNH Cl are dissolved in 65 ml. of water and brought to 100 ml. withconcentrated ammonia solution (CH.W. Biltz, Processes of QuantitativeAnalyses, Seventh edition, 1955, pages 89 and 90).

The use of the new process is not be considered limited in any way bythe examples presented herewith. It can be used for analytical purposeswherever there are reactions which involve heat effects, which depend onthe content of the substance to be determined in the test or in the teststream.

Without further analysis, the forgoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:

1. A process for effecting a thermometric analysis comprising the stepsof feeding a testsolution through tubing located in a thermostaticallycontrolled bath into a reaction vessel; feeding the reagent solutionthrough separate tubing located in the same thermostatically controlledbath into said reaction vessel, the reagent solution adapted to react,upon mixing, with at least one component of said test solution whilecausing a temperature change to take place as a result of said reaction,the said test solution and reagent solution entering the reaction vesselat a constant ratio and at an equal and constant temperature and thesaid reaction vessel being in heat exchange relationship with said bath;mixing said solutions to produce said temperature change by reaction ofsaid reagent solution with said test solution; and measuring saidtemperature change in said reaction vessel and bath, said temperaturechange being an indicator of a characteristic of said reaction takingplace in said reaction vessel.

2. The process of claim 1 wherein the said bath is maintained at aconstant temperature and the temperature change is measured in saidreaction vessel.

3. Process as defined in claim 1, wherein said tubing is composed of amaterial of high thermal conductivity and said vessel is composed of amaterial of lower thermal conductivity, allowing a more limited exchangeof heat.

4. Process as defined in claim 1, wherein said tubing is composed of ametal and is sufficientlylong so that the temperature of said solutionson reaching said reaction vessel is essentially equal to the temperatureof said bath, and said reaction vessel is composed of a materialselected from the group consisting of glass and plastics.

5. Process as defined in claim 1, wherein said temperature change iscompared with data derived in the calibration of said process, therebydetermining the value of said characteristic of said reacting componentof said test solution.

6. Process as defined in claim wherein said comparison is carried outautomatically, and said data are in the form of a calibration curve.

7. Process as defined in claim 1 wherein said test solution and saidreagent solution are fed continuously to said reaction vessel.

8. Process as defined in claim 1 wherein said reagent solution is fedcontinuously to said reaction vessel and said test solution isautomatically fed discontinuously to said reaction vessel.

9. Process as defined in claim 1 wherein said reaction between saidreagent solution and said test solution produces a precipitate and theresulting temperature change is determined.

10. Process as defined in claim 1 wherein said reagent solution and saidtest solution are highly concentrated.

11. Process as defined in claim 1 wherein the concentration of potassiumin a test solution is determined by feeding said test solutioncontaining a potassium salt, and a reagent solution containing sodiumperchlorate to said reaction vessel.

12. Process as defined in claim 1 wherein the concentration of magnesiumin a test solution is detering within said vessel; a probe fordetermining tempera-- ture within said vessel; automatic means forcomparing said temperature with previously derived calibration data;means for introducing at least one test solution to said reactionvessel; means for introducing at least one reagent solution to saidvessel; means for fast removal of said solutions and precipitates fromsaid reaction vessel subsequent to mixing in said reaCtion vessel; aconstant-temperature bath in which said reaction vessel which allows alimited exchange of heat with the bath is completely immersed and inwhich said test and reagent solutions are at least partially immersed;and pumping means for feeding said test and reagent solutions to saidreagent vessel.

1. A process for effecting a thermometric analysis comprising the stepsof feeding a test solution through tubing located in a thermostaticallycontrolled bath into a reaction vessel; feeding the reagent solutionthrough separate tubing located in the same thermostatically controlledbAth into said reaction vessel, the reagent solution adapted to react,upon mixing, with at least one component of said test solution whilecausing a temperature change to take place as a result of said reaction,the said test solution and reagent solution entering the reaction vesselat a constant ratio and at an equal and constant temperature and thesaid reaction vessel being in heat exchange relationship with said bath;mixing said solutions to produce said temperature change by reaction ofsaid reagent solution with said test solution; and measuring saidtemperature change in said reaction vessel and bath, said temperaturechange being an indicator of a characteristic of said reaction takingplace in said reaction vessel.
 2. The process of claim 1 wherein thesaid bath is maintained at a constant temperature and the temperaturechange is measured in said reaction vessel.
 3. Process as defined inclaim 1, wherein said tubing is composed of a material of high thermalconductivity and said vessel is composed of a material of lower thermalconductivity, allowing a more limited exchange of heat.
 4. Process asdefined in claim 1, wherein said tubing is composed of a metal and issufficiently long so that the temperature of said solutions on reachingsaid reaction vessel is essentially equal to the temperature of saidbath, and said reaction vessel is composed of a material selected fromthe group consisting of glass and plastics.
 5. Process as defined inclaim 1, wherein said temperature change is compared with data derivedin the calibration of said process, thereby determining the value ofsaid characteristic of said reacting component of said test solution. 6.Process as defined in claim 5 wherein said comparison is carried outautomatically, and said data are in the form of a calibration curve. 7.Process as defined in claim 1 wherein said test solution and saidreagent solution are fed continuously to said reaction vessel. 8.Process as defined in claim 1 wherein said reagent solution is fedcontinuously to said reaction vessel and said test solution isautomatically fed discontinuously to said reaction vessel.
 9. Process asdefined in claim 1 wherein said reaction between said reagent solutionand said test solution produces a precipitate and the resultingtemperature change is determined.
 10. Process as defined in claim 1wherein said reagent solution and said test solution are highlyconcentrated.
 11. Process as defined in claim 1 wherein theconcentration of potassium in a test solution is determined by feedingsaid test solution containing a potassium salt, and a reagent solutioncontaining sodium perchlorate to said reaction vessel.
 12. Process asdefined in claim 1 wherein the concentration of magnesium in a testsolution is determined by feeding said test solution made alkaline withammonia and containing a magnesium salt, and said reagent solutioncontaining a salt selected from the group consisting of ammoniumdihydrogen phosphate and sodium dihydrogen phosphate to said reactionvessel.
 13. Process as defined in claim 1 for determining the phosphatecontent of a test solution by feeding a phosphate-containing testsolution and a reagent solution made alkaline with ammonia andcontaining a magnesium compound to said reaction vessel.